Fixed in commit https://github.com/JiriBilek/WiFiSpi/tree/4d12b26c8c5e80786d972e845f90f7bb858427b0Please get new version of master library and try again.
I'm glad if I was able to be assistance. Judging from what I've seen of the library and the quality of your support on this thread, I think it will be a very welcome addition!
the Library Manager will not help to get the latest fixes.
to update from GitHub, use git